revtothelimit - motorbike forum

David wrote: Thu Aug 19, 2021 9:18 am Someone (not me, Guv) is going to say MTFU, put your big boots on and give it a go. Are there any big hills by you?

I tried rolling down the small hill on my street, the rear wheel just locks up as soon as you drop the clutch - I tried in all four gears, just to be sure.

I know you can 'bounce' it to get more rear wheel grip when you drop the clutch but that presumably requires a knack too.

Mr. Dazzle wrote: Thu Aug 19, 2021 8:26 am I've e-mailed the guy who did this original head repair....

https://vintageclassicmotorcycles.co.uk

I can feel myself getting fucked of with this bike, so it's time to call in someone else

Callow yoof in lack of staying power shocker! Hah! Some of us only had these sorts of bikes available to us as our only transport* back when you had to bang rocks together to start a fire.

Seriously though, you're probably 95% there and your chap will probably go 'Ahah! You numbat, you've.......twiddle, kick, brrrrrmmm'.

*Probably didn't put high-comp pistons in the daily workhorse though.

PS 'Bump' start. I always assumed it was called that because you jumped on and bumped your whole weight on it to get that grip (if needed). Easier and less precarious to get someone to give you a shove/use a hill.

My wife's uncle dispatched on this bike in the 80s. High comp pistons, close ratio box and all.

Your valve springs aren't getting 'coil bound' are they? Happened to my old Sunbeam Stiletto when I put the high lift cam in a standard head.

I doubt it, for two reasons: The engine turns over fine 'in isolation' and it's had the same cams for 50 years with no problems.

If the engine turns over fine and the gearbox turns over fine, the only thing left is the primary drive, surely?

Hairybiker84 wrote: Thu Aug 19, 2021 10:01 am If the engine turns over fine and the gearbox turns over fine, the only thing left is the primary drive, surely?

Or something in the gearbox/primary which only shows up under load. So for example the gearbox mainshaft could be out of alignment/bent/whatever so it spins OK when it's "free" but when you try and put load on it - either by turning the engine via the wheel, or by using it to turn the engine over with the kicker - the extra drag shows up. Apparently it's not uncommon for gear bushes to wear out and cause such effects.

Half of me thinks I'm being a fanny, half of my is suspicious of the fact it's still hard to kick over even with the plugs out. And the fact it's hard to turn over via the wheel, again with the plugs out. When I say 'hard to turn over', if I sit facing the wheel with one hand at 9 and the other at 3 and the bike in 4th, I can turn hard enough that I'll either push the bike forward off the centre stand, or lift the front wheel off the ground and start dragging it backwards, without turning teh engine over. The only way to turn it over is to 'jerk' the wheel, which doens't feel healthy.

As above though, turning the engine over at the crank is simple enough. It's also reasonably easy to turn if over with a socket on teh nut in the middle of the clutch. Putting a socket on the other end of the main shaft (on the RHS of the bike) and turning it over is much harder.

Mr. Dazzle wrote: Thu Aug 19, 2021 9:59 am I doubt it, for two reasons: The engine turns over fine 'in isolation' and it's had the same cams for 50 years with no problems.

And when you turn the engine at the crank, everything 'behind' turns nicely - timing chain etc etc?

Probably totally off the wall, but if it does, I wonder if you can turn it at the crank, in gear. Logically (?) that would mean it's either the kickstart that's the problem or there isn't a problem. An expert will probably point and laugh at me shortly.....

The sleeve gear bush between the mainshaft and the output hollow shaft does wear, but that doesn’t have much effect.

Mr. Dazzle wrote: Thu Aug 19, 2021 8:33 am Well even if it is just tight, the guy who makes a living fixing old Brit Iron will have "the knack" much better than old soft palms Dazzle 'ere.

By way of comparison, I also have a 1965 5TA in the garage. That's a 500cc engine with much lower compression than the Bonnie (7:1 I think). It's also got a much shorter kicker. I can turn that over, plugs in, by hand.

With plugs out, the 500 and the 650 should feel similar.

New piston rings make it stiffer, but not drastically.

Chain alignment and wear and then tensioner face would be my next things to check.
You said that the kick start is 'floppy' that to me implies that the bushes/shaft has play, if you try and turn gears that aren't meshed correctly the force required is significantly increased, often to the point of jamming entirely or skipping completely.

I checked, the floppyness was the lever/pivot which I've managed to tighten. Now I've put the gearbox outer cover back on it's much tighter.

Is the primary chain properly in line?

It should not be tighter with the cover on .

Perhaps the kick start bush is loose or fubarred.

Have you tried re-routing power through the main deflector?

David wrote: Thu Aug 19, 2021 10:45 am It should not be tighter with the cover on .

Badly worded. The floppyness was the lever to the pivot. I took the cover off to check, now the cover is back on the lever is not floppy. The kicker gears look good and are meshing OK I think.

KungFooBob wrote: Thu Aug 19, 2021 10:49 am Have you tried re-routing power through the main deflector?

The core ejection system is the least reliable thing on the whole ship isn't it? Why can't they make it work as well as the lights and gravity? Those never fail.

Big boots time....please video it.

Get Derek the Badger to tow start you with his KX500...